example for auto build seems outdated.

[Lachstec]

I am using cornucopia in a project of mine and oriented myself on the example examples/auto_build. It seems that the example is slightly outdated. I just copied the example, and then the compiler told me that I passed a &[&str; 1] where a Vec<String> was expected.

I think that the example needs to be updated and would submit a PR if the example is truly outdated.